Method for forming metal oxide coating film and vapor deposition apparatus

Abstract

A photocatalytic composite material having a photocatalytic titanium oxide film on the surface of a substrate is produced by a CVD method in which TiCl₄ vapor is reacted with water vapor. The TiCl₄ vapor and the water vapor are injected into a vapor deposition chamber (9) through nozzles (5) and (6), respectively, such that the resulting two injected vapor streams meet before reaching the substrate, thereby mixing the two vapors. Within 3 seconds after this mixing, the mixed vapors are brought into contact with a substrate (1) which is moving in one direction. Preferably the TiCl₄ vapor is injected in a reverse direction with respect to the direction of movement of the substrate through a multi-orifice nozzle (5), while the water vapor is injected through a slit nozzle (6) disposed at a smaller angle with respect to the substrate.

Description

TECHNICAL FIELD [0001] This invention relates to a process for forming a metal oxide film such as a titanium oxide film having a photocatalytic activity on the surface of a substrate by the CVD (chemical vapor deposition) technique, and to a vapor deposition apparatus which is suitable for use in this film forming process. BACKGROUND ART [0002] The photocatalytic activity exhibited by titanium oxide has attracted attention in that it is effective for various environmental depollution treatments including deodorization, prevention of microbial growth, and prevention of fouling. In order to allow the photocatalytic activity of titanium oxide to be exerted, photocatalytic titanium oxide composite materials have been developed in which a film of a photocatalytic titanium oxide is formed on the surface of a substrate selected from a wide variety of materials. [0003] Practical methods for the formation of a titanium oxide film for use as a photocatalyst are roughly classified into an appl...

AI Technical Summary

Benefits of technology

[0012] The present inventors investigated the above-described CVD film formation method from the new point of view that the progress of a reaction of TiCl4 and H2O in the gas phase is suppressed by controlling contact of TiCl4 vapor supplied as a reactant with water vapor. As a result, it was found that injection of jetted streams of both the TiCl4 vapor and the water vapor through respective nozzles makes it possible to control the time at which these two vapors are allowed to contact and mix, which in turn makes it possible to control within a proper range the time elapsed from mixing of the two vapors until the mixed vapors contact a substrate, thereby significantly preventing a reaction between TiCl4 and H2O from proceeding in the gas phase and leading to elimination of the above-described problems.

[0013] Specifically, by bringing TiCl4 vapor into contact with a substrate within 3 seconds and preferably within one second from its mixing with water vapor, the occurrence of a hydrolysis reaction of TiCl4 in locations other than at the surface of the substrate can be suppressed. Thus, a significant improvement in the rate of film formation and in the utilization factor of TiCl4 for film formation is achieved, and it is made possible to form a titanium oxide film having a uniform thickness and good appearance.

[0014] Although the reason for this has not been elucidated completely, it is thought that due to limitation of the time from contact and mixing of the two vapors by collision before they reach the substrate as described above, the two vapors may arrive at the surface of the substrate while they are mixed only on a macroscopic scale but not completely mixed on a microscopic scale (hence, such that a reaction between TiCl4 and H2O is suppressed). It is also conceivable that the possibility of TiCl4 vapor contacting the substrate is increased, which contributes to an improved rate of film formation.

Problems solved by technology

In the formation of a titanium oxide film by the CVD technique using hydrolysis of TiCl4, a very high reactivity between TiCl4 vapor and water vapor allows the TiCl4 vapor to prematurely react with the water vapor in the gas phase (namely, in the gas space within a vapor deposition chamber) before it reaches a substrate, which causes the above-described various problems.

As a result, TiCl4 vapor fed into the vapor deposition chamber immediately reacted with water vapor which existed in its surroundings, and a hydrolysis reaction in the gas phase could not be controlled.

Images